1. Field of the Invention
The invention generally relates to the field of photography. More particularly, it relates to a dual lens camera of the type wherein a relatively long focal length lens and a relatively short focal length lens are selectively used to expose film in the camera, for example to take a telephoto or a wide angle picture.
2. Description of the Prior Art
Dual lens cameras typical of the prior art are disclosed in U.S. Pat. No. 4,527,874, granted July 9, 1984, and U.S. Pat. No. 4,609,270, granted Sept. 2, 1986. Such a camera often has a relatively long focal length lens and a relatively short focal length lens, either one of which is selectively used for telephoto and wide angle photography. A fixed mirror is permanently located behind the long focal length lens and a movable mirror is positionable in facing parallel relation to the fixed mirror, either behind the long focal length lens or behind an opening for that lens in the front wall of the camera. The movable mirror in this position has a matte black coating on its rear side which is disposed to block ambient light entering the short focal length lens or the wall opening to prevent the light from reaching an exposure aperture covered by a back door of the camera. At the same time, the two mirrors cooperate to define a Z-shaped light-ray path (i.e., one that bends at angles of less than 90.degree.) from the long focal length lens to the exposure aperture. Alternatively, the movable mirror may be pivoted out of its blocking position behind the short focal length lens or the wall opening to a non-blocking position to allow ambient light entering the short focal length lens to pass straight through to the exposure aperture. In the non-blocking position, the movable mirror deflects ambient light reflected by the fixed mirror from the long focal length lens to prevent the light from reaching the exposure aperture. Thus the alternate positions of the movable mirror determine which one of the two lenses is used.
In the dual lens camera disclosed in U.S. Pat. No. 4,527,874, the back door is opened to uncover the exposure aperture to facilitate film loading and unloading. However, when the door is opened and the movable mirror is in its blocking position parallel to the fixed mirror, the reflective surfaces of the two mirrors are generally accessible through the exposure aperture. This is disadvantageous in that it allows dust or other foreign particles which might enter the exposure aperture to reach the reflective surfaces. Moreover, it allows the reflective surfaces to be inadvertently touched and thereby smeared. Conversely, when the door is opened and the movable mirror is in its non-blocking position, the reflective surface of the movable mirror is disposed in shielding relation with the reflective surface of the fixed mirror, making the reflective surfaces of the two mirrors substantially inaccessible through the exposure aperture. This is advantageous in that it prevents dust or other foreign particles which might enter the exposure aperture from reaching the reflective surfaces. Moreover, it prevents the reflective surfaces from being inadvertently touched.
In the dual lens camera disclosed in U.S. Pat. No. 4,609,270, a lens cover is alternately rotatable in opposite directions from an intermediate position covering the long focal length lens and the short focal length lens to respective positions uncovering either of the lenses. When the lens cover is rotated from its position uncovering the short focal length lens to its intermediate position, the movable mirror remains in its non-blocking position. If the back cover is thereafter opened, the reflective surfaces of the two mirrors are substantially inaccessible through the exposure aperture. However, when the lens cover is rotated from its position covering the long focal length lens to its intermediate position, the movable mirror remains in its blocking position. If the back cover is then opened, the reflective surfaces of the two mirrors are generally accessible through the exposure aperture.
Accordingly, in known dual lens cameras, the reflective surfaces of the movable and fixed mirrors are not always shielded against foreign particles or touch when the rear door is opened. This allows the reflective surfaces to be possibly damaged by touch or to be possibly rendered ineffective, or less effective, by dust or other foreign matter.